There are a handful of parametric models that have successfully served as population models for failure times arising from a wide range of products and failure mechanisms. Sometimes there are probabilistic arguments based on the physics of the failure mode that tend to justify the choice of model. Other times the model is used solely because of its  empirical success fitting actual failure data. 

Seven models will be described in this section: 

1. The Exponential
2. The Weibull
3. The Extreme Value 
4. The Lognormal
5. The Gamma 
6. The Birnbaum-Saunders Model
7. The Proportional hazards Model